There is a high demand for functional bone grafts in the United States, as well as in other countries worldwide. More than half a million patients receive bone defect treatments in the United States per year and it costs more than $2.5 billion. This situation is expected to double by 2020 in the United States and in other countries due to many factors, including the growing needs of the increasing populations and increased life expectancy.
Tissue engineering has become an exciting and multidisciplinary field aiming to develop tissues and organs to replace or regenerate defective tissues for almost three decades. Cells, scaffolds and growth-stimulating signals are basic and essential components of the tissue engineering to develop engineered tissues.
Many synthetic materials have been used in the aim of producing scaffolds including polystyrene, poly-l-lactic acid (PLLA), polyglycolic acid (PGA) and poly-dl-lactic-coglycolic acid (PLGA). These materials have shown much success as they can be fabricated with a designed architecture. In addition, their degradation properties can be controlled by changing the polymer concentrations however they have drawbacks including the risk of rejection due to reduced bioactivity.
Another approach to produce scaffold biomaterials is the use of biological materials. Biological polymers such as collagen, proteoglycans, alginate and chitosan have been used in the production of scaffolds for tissue engineering. Unlike synthetic polymer-based scaffolds, natural polymers are biologically active and have properties to promote cell adhesion and growth. In addition, they are also biodegradable and therefore host cells have enough time to produce their own extracellular matrix and replace the degraded scaffold.
However, it is still a challenge to produce scaffolds from biological materials with homogeneous and reproducible structures. Furthermore, the scaffolds which are produced by using biological materials generally have poor mechanical properties and therefore their poor mechanical properties limit their use in, for example, load bearing orthopedic applications.
Transplantation is another approach to provide substitute tissues and organs for defective tissues and organs. However, transplants have serious drawbacks due to problems with providing enough tissue for all of the patients who require them and there are risks of rejection by the patient's immune system. There is also possibility of introducing infection or disease from the donor to the patient. In addition, immune-suppressor drugs should be used after transplantation to prevent organ rejections which make the patients susceptible to many pathogens.
A promising approach to produce functional substitute organs and tissues has emerged in recent years. Decellularization of allogeneic or xenogeneic donor organs such as heart, liver and lung, provides acellular biologic scaffold materials which retain their natural three-dimensional structures. This approach provides the opportunity for direct vascular connection of donor organ to vascular system of the patient.
Particularly difficult is the decellularization of bone tissue. The term “bone tissue” refers specifically to the mineral matrix that form the rigid sections of the organ “bone”. There are two types of bone tissue: cortical bone and cancellous bone. Cortical bone is compact, while cancellous bone has a trabecular and spongy structure. The tissues are biologically identical; the difference is in how the microstructure is arranged.
Unlike soft tissue and organs, in view of the structure and the mineralization of the bone tissue, it is a difficult procedure to remove all cells (i.e. decellularize) from bone tissue. In fact, bone cells (osteoblasts, osteocytes and osteoclasts) are embedded in very tightly packed units which are called lacunae; therefore, it is very difficult to perform a complete decellularization of the bone tissue.
US2013/0337560 disclose a method of decellularization of native bone, for example a bone having cortical bone, cancellous bone, a central (medullary)cavity, and cells. In order to decellularize that native bone, one or more apertures are introduced from the exterior of the bone into the central cavity. One or more disruption media are perfused into the central cavity of the bone under condition that provide for decellularization of bone. The medium having cells and/or cellular debris can than flow out of the native arterial and/or venous structures in the bone. However, there is the possibility of remaining cellular components after application of disruption media through holes to larger portions of the bone. Therefore, also in view of the particular microstructure of the bone tissue, the decellularization of bone tissue results very difficult.
Furthermore, the selection of the disruption media to be used can be difficult. In fact, the use of one or more agents and the type of agents used may provide different final decellularization results.